In the case of specific burners, for example in the case of premix burners, gaseous and/or liquid fuel can be introduced by a lance. As a rule, the fuel which is introduced via the lance serves for stabilizing a flame front in the combustion chamber or for a pilot operation of the combustion chamber. In the case of a special type of construction, the respective lance has a foot and also a cylindrical shank which projects from it essentially at right angles. Via the foot, the lance is supported on a burner wall in such a way that the foot extends transversely to a main flow direction of the burner, whereas the shank extends essentially centrally in the burner parallel to the main flow direction. For the introduction of the gaseous fuel, the lance is equipped with at least one nozzle on its shank.
Conventional burners, as are disclosed in EP0623786, operate as a rule with natural gas as gaseous fuel which is introduced via the lance into the burner. For a favorable mixing with the air which flows through the burner in its main throughflow direction, it has proved favorable to inject the fuel radially into the burner with regard to a longitudinal center axis of the shank, an example of which is disclosed in EP1030109.
The requirements for emissions at high hot gas temperatures and during partial load operation, and also for flexibility in operating behavior, have increased in recent years. Furthermore, in addition to air, installations in which additional oxidator gases are used for combustion of the fuel are also increasingly proposed. In addition to air, an oxidator gas for example can be a gas mixture which is obtained as a result of exhaust gas recirculation, or for example it can be an oxygenous product of an air separation plant.
It has been shown that with conventional burners and conventional lances the NOx emissions in the case of increasing hot gas temperature cannot be kept at a low level without great detriment in the case of partial load emissions and in pulsation behavior. Without further optimization, the fuels in the case of the required increased hot gas temperatures react with the oxidator gas before an adequate mixing is carried out, as a result of which on the one hand increased pollutant emissions can be established, and as a result of which on the other hand an increased risk of damage to the burner ensues due to flame flashback. If the fuel injection is optimized so that an adequate mixing for a low-emissions operation at the maximum hot gas temperature can be realized, then during partial load operation this leads to an extremely lean combustion with high CO emissions. Furthermore, the stability of the combustion is difficult to ensure, which can be manifested in harmful combustion chamber pulsations.
A similar problem also arises during the combustion of fuels which contain a comparatively high proportion of hydrogen gas and carbon monoxide gas. Such fuels, which for example can be formed as a result of a partial oxidation of conventional hydrocarbons, are also referred to as synthesis gas or syngas. Such fuels are characterized by a significantly increased reactivity compared with conventional fuels. Hydrogen and carbon monoxide react with oxygen much quicker and at already lower temperatures than carbonaceous fuels, such as natural gas, so that, just as in the case of the aforementioned increase of the hot gas temperature, the combustible gases react before an adequate mixing.